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Old 13th September 2007, 11:24 PM   #31
fotios is offline fotios  Greece
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Only because i am interested about this thread.
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Old 13th September 2007, 11:45 PM   #32
rdf is offline rdf  Canada
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Quote:
Originally posted by Conrad Hoffman
I don't have the answer, but wonder what it would take in terms of caps and their type, to create a high value (100uF or so) composite cap that would maintain all it's parameters to 100khz or so?
H Conrad. Take this one for a spin. Consider a cap with, let's say, two bypasses. A general rule of thumb I work with is any bypass much smaller than a 1/10th the main cap risks resonating against the main's parasitic. Now preceed each of the three caps with an inductor sized on the same order as the following cap's inductance. Take a look at the total network's effect on PS filtering and the effective source impedance looking back from the load.

As an example, a 100uF with 30nH primary inductance bypassed with 10uf/20nH and 1uF/15nH. Adjust nH to taste to account for traces, etc.. So the power supply filtering (after the rectification cap) becomes:

30nH > 100uF > 20nH > 10uF > 15nH > 1uF > load
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Old 14th September 2007, 12:25 AM   #33
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That looks dangerously like a circuit dreamed up by a tube guy! The Ls solves some problems I was having with simple bypassing, if the DCR is kept very low. Shouldn't be any problem at these values. I have everything handy to actually measure this, and will try it in the next few days. Thanks!
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Old 14th September 2007, 12:28 AM   #34
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Quote:
Originally posted by maxlorenz

Particularly, I have modded a cheap multiformat player, with a 0u1 polypropilene cap across the leads of the "big" (around 150uF) main SMPS electrolytic cap, with good effect (but I also swapped the rectifier diodes to low recovery types).
Any lights about this will be welcome
I'd recommend a larger poly cap, something like 0.47 uF to 1.0 uF. Bypass ratios of 1500:1 make me nervous about parallel resonances.
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Old 14th September 2007, 12:54 AM   #35
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Quote:
I'd recommend a larger poly cap, something like 0.47 uF to 1.0 uF. Bypass ratios of 1500:1 make me nervous about parallel resonances.
OK. Thanks for that.

M
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Old 14th September 2007, 01:13 AM   #36
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Quote:
Originally posted by maxlorenz


OK. Thanks for that.

M
I'm interested in how this would affect your perception of the unit. Please tell us if you notice a change.
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Old 14th September 2007, 02:19 AM   #37
rdf is offline rdf  Canada
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Quote:
Originally posted by Conrad Hoffman
That looks dangerously like a circuit dreamed up by a tube guy!
Guilty as charged. I'll take that as a complement. Naturally as such I didn't think about large currents but it should work well for preamps, low power amps, etc. If the target is lowering HF PS impedance for reasons of stability no reason a small 'RF' bypass won't work with a large main cap jumps out. I wouldn't build a glass circuit without using this technique, to my ....perception it always brings clear benefits.
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Old 14th September 2007, 07:51 AM   #38
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by rdf
...........Take a look at the total network's effect on PS filtering and the effective source impedance looking back from the load.

As an example, a 100uF with 30nH primary inductance bypassed with 10uf/20nH and 1uF/15nH. Adjust nH to taste to account for traces, etc.. So the power supply filtering (after the rectification cap) becomes:

30nH > 100uF > 20nH > 10uF > 15nH > 1uF > load
these two latter inductances look quite small.
Can the inductances be the wire interconnecting the main electros to the main circuit board? 1uf at the circuit and 10uF half way along the PSU to circuit board cable pair.
The snubbered Carlos PSU may mimic this topology where he has shown an RC at the output of the PSU and a further C at the circuit board.
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Old 14th September 2007, 01:31 PM   #39
Eva is offline Eva  Spain
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This once was an interesting thread
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Old 14th September 2007, 05:10 PM   #40
rdf is offline rdf  Canada
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And now it's back to bypassing large caps with small, why the tears?
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